The most striking thing about the Miasole solar cell production plant in San Jose is how much of it is empty.
....But if Miasole's plan comes together, within a couple of years it will house a production line turning out vast rolls of photovoltaic cells, that some believe could help put solar power on a par with coal, gas or oil.
"It's an enormous growth opportunity," says chief executive officer David Pearce, matter-of-factly.
His company is just one of dozens in California at the cutting edge of innovation in renewable fuels.
.... The boom is funding various clean energy projects, from developing hydrogen fuel cells to turning algae into fuel and creating synthetic fuels through biological engineering.
And the search for solutions to the climate crisis does not just involve energy.
California firm Planktos is investigating a controversial technique to absorb carbon dioxide by stimulating plankton growth in the oceans.
If the idea has as much potential as Planktos boss Russ George believes, it could go a significant way towards reversing global warming all on its own.
In doing so, it could earn the firm millions through the carbon market, by selling credits to firms emitting greenhouse gases.
....it is the clean tech sector's soaring share prices, and the possibility of big returns, that is fuelling the investment boom.
The clean tech sector is "exploding, especially in the US", says Torsten Merkel, European director of Cleantech Group, which advises investors.
....Many credit California's politicians for providing the stimulus.
"I think it's fair to say the [solar] industry would not exist in a meaningful way, were it not for subsidies," says Miasole CEO David Pearce.
California is putting $3bn into a 10-year programme to put solar panels on a million roofs, while the federal government chips in 30% of the installation costs.
The state has mandated that 20% of its electricity must come from renewable sources by 2010.
It has also written big cuts in greenhouse gases into law, and is laying the foundations for a carbon market that would reward firms for cutting emissions.
It means companies that find new ways to beat global warming are going to be very popular.